This invention relates to a process for producing tris(tribromophenoxy)-s-triazine.
Tris(tribromophenoxy)-s-triazine compounds as such are known from French Patent 1566675. It is also known from U.S. Pat. No. 3,843,650 and Japanese Kokai Patent Publication No. 47-25232 that these compounds have very satisfactory properties for application as flame retardant additives to synthetic resins. However, tris(tribromophenoxy)-s-triazine compounds as described in French Patent 1566675 were of low purity and could be made available only in low yield.
The technology for production of tris(tribromophenoxy)-s-triazine, thus far known from Japanese Kokai Patent Publication No. 47-25232 and U.S. Pat. No. 3,843,650, comprises dissolving cyanuric chloride in a ketone or cyclic ether solvent and adding an aqueous or ethanolic solution of a tribromophenolate. An alternative process, disclosed in JP Kokai No. 53-116390, comprises an alkali treatment in the presence of a phase transfer catalyst in a heterogeneous solvent system consisting of water and an organic solvent.
However, in the production system employing a hydrophilic solvent, solvent recovery entails the azeotropic inclusion of water in the recovered solvent and this water can hardly be removed from the solvent. If the recovered solvent is reused in the reaction, the charge cyanuric chloride is hydrolyzed and the resulting hydrolyzate contaminates the reaction system. This causes a decreased purity of the product compound and, when such product is added to synthetic resin, both the physical properties and flame resistance of the resin are adversely affected.
In the production system employing a non-hydrophilic solvent, as described in Japanese Kokai Patent Publication No. 3-34972, tris(tribromophenoxy)-s-triazine of high purity can be obtained in high yield but prolonged aging was essential for carrying the reaction to completion. However, when the tribromophenolate-cyanuric chloride reaction system involves an extended period of aging, cyanuric chloride is hydrolyzed by water in its reaction with the tribromophenolate so that the product tris(tribromophenoxy)-s-triazine cannot be of high purity. To overcome this disadvantage, in the production process employing a non-hydrophilic solvent, it might be contemplated to use a phase transfer catalyst in an increased amount. However, the phase transfer catalyst is so expensive that it is uneconomical to use it in a large amount and actually an increase in the amount of a phase transfer catalyst contributes little to a reduction in reaction time.